Refrigeration systems operable at low condenser pressures



Dec. 15, 1964 L. MAcRow 3,161,029

REFRIGERATION SYSTEMS OPERABLE AT LOW-CONDENSER PRESSURES Filed Oct. 4, 1962 INVENTOR.

LAWRENCE MACROW.

ATTORNEY.

United States Patent 3,161,029 v REFRIGERATHUN SYSTEMS; OPERABLE AT DOW CQNDENSER PRESSURE? Lawrence Marrow, Elma, N.Y., assignor to Carrier Corpoiation, Syracuse, N .Y., a corporation of Delaware Filed Oct. 4, 1962, Ser. No. 228,430 1 Claim. ((Jl. 62197) The present invention relates to improved refrigeration systems which will provide refrigeration at low condenser pressures.

A conventional refrigeration system includes a closed circuit having a compressor, condenser, expansion means and evaporator in series. Gaseous refrigerant is pum ed by the compressor to the condenser, the gaseous refrigerant being placed in heat exchange relation with a cooling medium such as water or ambient air in the condenser to condense the's'ame. Under normal operating conditions within a predetermined range of ambient temperatures, the refrigerant in the condenser, after said cooling has occurred, remains at a sufficiently high pressure tov force the liquefied refrigerant through the expansion means to the evaporator. In the evaporator, heat is absorbed from the area in which the evaporator is located, thus evaporating the liquid refrigerant, gaseous refrigerant returning to the compressor. However, when the ambient temperature of the cooling medium, which is utilized to condense the compressed gases in the condenser, drops below said predetermined range of temperatures, the gases in the condenser condense to a relatively great extent and therefore a condition may arise where there is insufiicient pressure in the condenser to effect satisfactory fiow of the refrigerant through the expansion means.

In the past, it has been proposed to raise the condenser or head pressure of the refrigeration system in order to cause proper flow of refrigerant through the refrigeration circuit when the condenser pressure was below a predetermined value. Increased condenser pressures were required because the expansion valve of a conventional refrigeration system could not provide proper refrigerant flow at the low condenser pressures which accompanied low condensing temperatures. Various arrangements for raising the condenser pressure were suggested, including the effecting of refrigerant hang-up in the condenser to theieby decrease the effective area thereof which was (utilized for condensing and thereby maintaining the pressure in the condenser at a satisfactory value for proper expansion valve operation. These arrangements not only required complicated and costly controls, but also caused the refrigeration systems in which they were located to operate at decreased efficiency. This decreased efiiciency resulted from the compressor operating against a raised condenser pressure which was in excess of the low condenser pressure which could be realized at low ambient temperatures.

The primary object of the present invention is to provide a refrigeration system which will operate at low condenser pressures, thereby dispensing with the complicated and costly controls heretofore used for raising condenser pressures.

Another object of the present invention is to provide refrigeration systems which will function efiiciently at extremely low condenser pressures.

A still further object of the present invention is to provide refrigeration systems which permit the use of low condenser pressures by eliminating the need for the expansion means which required relatively high condenser pressures for proper operation. Other objects and attendant advantages of the present invention will readily be perceived hereafter.

This invention relates to a refrigeration system comprising in combination a compressor, a condenser, expan- 3,161,029 Patented Dec. 15, 1964 sion means, and an evaporator in a series-closed circuit relationship, circuit means for passing substantially only liquid refrigerant from said condenser into said evaporator when the pressure in said condenser falls below a predetermined value which is suflicient to force refrigerant from said condenser through said expansion means to said evaporator, thereby permitting said refrigeration system to operate at condenser pressures which are below said predetermined value, said circuit means being located in bypass relationship to said expansion means, a valve only in said circuit means, said 'valve when open permitting liquid refrigerant to bypass said expansion means and flow directly from said condenser to said evaporator through said circuit means and therefore flood said evaporator, control means for opening said valve when said condenser pressure is below said predetermined value and for closing said valve when said condenser pressure is above predetermined value.

The attached drawing is a schematic view of an embodiment of a refrigeration system incorporating the principles of the instant invention.

In the figure, a compressor 10 is shown which cornpre'sses gaseous refrigerant and transmits it to the inlet of condenser 11 through line 12. Fan 11' passes ambient cooling air in heat exchange relationship with refrigerant in the condenser to condense the same. When the condenser pressure is sufficiently high, condensed refrigerant will be forced from condenser 11 into line 14 leading to thermal expansion valve 13. Thermal expansion valve 13 is regulated by means of thermal sensing bulb I3, placed adjacent line 19, in communication therewith through capillary 15. After refrigerant flows through thermal expansion valve 13, it flows into line 16 leading to evaporator 17. The evaporation of refrigerant in evaporator 17 absorbs heat from the surroundings in which said evaporator is located. The outlet of evaporator 17 is in communication with accumulator 18 through line 19. Refrigerant leaving evaporator 17 passes into accumulator I8, liquid refrigerant settling to the bottom of said accumulator 18 and gaseous refrigerant passing from accumulator 18 to compressor 10 through line 20. A fan 21 causes air from the surroundings to be cooled to pass over evaporator 17. Fans 11 and 21 are placed in the refrigerat-ion circuit in the conventional manner and have suitable electrical connections thereto, not shown.

A by-pass circuit including line 22, pressure controlled valve 23, and line 24 is placed in parallel with the thermal expansion valve 13, line 22 being in communication with line 14 leading to thermal expansion valve 13 and line 24 being in communication with line 16 leading from thermal expansion valve 13. When the condenser pressure is above a predetermined value which is sufficient to force refrigerant through thermal expansion valve 13, the condenser pressure will also cause pressure responsive valve 23 to be closed because the latter is in communication with condenser 11 through capillary 25. If desired, valve 23 may be responsive to condenser temperature rather than condenser pressure. Under the foregoing circumstances, the refrigeration system will operate in its normal conventional manner and there will be no flow of refrigerant through the by-pass circuit.

However, when the ambient air temperature, which is utilized to cool condenser 11, falls below a predetermined value, the pressure of refrigerant in the condenser may drop to a value which is insuiiicient to force refrigerant through thermal expansion valve 13. This decreased pressure will also be communicated to pressure responsive valve 23 through line 25 and cause said valve to open, thereby permitting a by-pass circuit to be established about thermal expansion vave 13 through line 22, valve 23, and line 24. Thus, liquid refrigerant from condenser 11 may flow directly into evaporator 17 through said bypass circuit to thereby flood said evaporator. The flooding of said evaporator with liquid refrigerant is sufficient to provide a refrigeration effect whereby evaporator 17 absorbs heat from the area in which it is located. It will be noted that this refrigeration effect is obtained without raising the pressure of refrigerant in condenser 11 above a value which corresopnds to the temperature thereof. The mixture of liquid and gaseous refrigerant leaving evaporator 17 passes into accumulator 18 through line 19, the liquid refrigerant settling to the bottom of accumulator 18 and the gaseous refrigerant above the level 26 of the liquid in accumulator 18 passing to compressor 10 through line 20.

The by-pass circuit will operate in the foregoing manner until such time as the condenser pressure is raised to a sufficiently high value which will close pressure responsive. valve 23 and permit thermal expansion valve 13 to assume its normal function.

While a preferred embodiment of the present invention has been disclosed, it will readily be understood that the present invention is not to be limited thereto, but may be otherwise embodied within the scope of the following claim.

I claim:

In a refrigeration system, the combination of a compressor, a condenser, expansion means, and an evaporator in a series-closed circuit relationship, circuit means for passing substantially only liquid refrigerant from said condenser into said evaporator when the pressure in said condenser falls below a predetermined value which is sufficient to force refrigerant from said condenser through said expansion means to said evaporator, thereby permitting said refrigeration system to operate at condenser pressures which are below said predetermined value, said circuit means being located in bypass relationship to said expansion means, a valve only in said circuit means, said valve when open permitting liquid refrigerant to bypass said expansion means and flow directly from said condenser to said evaporator through said circuit means and therefore flood said evaporator, control means for opening said valve when said condenser pressure is below said predetermined value and for closing said valve when said condenser pressure is above predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 2,359,595 Urban Oct. 3, 1944 2,675,683 MeGrath Apr. 20, 1954 2,949,750 Kramer Aug. 23, 1960 3,031,859 Mann May 1, 1962 3,081,606 Brose Mar. 19, 1963 

